The creators of the Father Ted television series have denounced Ireland's proposed blasphemy laws as "insanity" and pledged to support a campaign to repeal them.

Arthur Mathews and Graham Linehan backed moves by a group of Irish secularists to challenge the bill against blasphemy introduced in the Dáil last week. Atheist Ireland said this weekend that it will publish a statement blaspheming all the major religions in Ireland, including Christianity and Islam. The group said it would be a calculated challenge to the law.

Under the Irish constitution, the state is obliged to have blasphemy laws. The bill going through the Dáil would amend the Defamation Act of 1961, which includes blasphemy as a crime. To abolish blasphemy laws, the government would have to hold a referendum to amend the constitution. The duo, who wrote a host of other TV comedies such as Big Train, described the blasphemy law contained in the new bill covering defamation in Ireland as "a return to the Middle Ages".

Linehan told the Observer that the justice minister Dermot Ahern, who introduced the bill, should be challenged to define what he meant by blasphemy. "This is insanity. Please, Mr Ahern, define the things we can't say, please! Can we say, 'Jesus is gay'? Or can we ask, 'Is God in a biscuit?' Could he tell us what it means? It is just insanity. After all, there are things contained in the holy books of one religion that are blasphemy to another religion. The logic behind this comes from Alice in Wonderland." He said the Irish blasphemy law was part of a trend in the west where freedom of expression was being attacked "to placate the craziest people on earth".

Linehan said that technically, under the new bill, certain scenes from Father Ted could be deemed blasphemous. "In Ted we kind of generally avoided central tenets of belief, because it was not what the show was about. It was about a very bad priest who didn't think about religion a lot. Writers should not be looking over their shoulders. If you are writing a satire today, the Irish government are making it harder to do that."

Mathews said the bill "hardly seems necessary in the Ireland of the 21st century ... It's a pity that law hadn't been introduced when we were writing Father Ted, because it would have given us a great storyline. The best attitude to this nonsense is to laugh at it and send it up. There is no popular clamour for it in Ireland, so I wonder why Dermot Ahern has brought it in the first place."

Michael Nugent, of Atheist Ireland, who has also written comedy with Mathews, said the bill was silly and dangerous. "It is silly because it revives a medieval religious law in a modern pluralist republic, and it makes Ireland seem like a backward country. People need protection. Ideas do not. Ideas should always be open to criticism and ridicule. If the law is passed, we will be immediately testing it by publishing a blasphemous statement."

Nugent pointed out that in 1909 George Bernard Shaw had a play banned for blasphemy. "He defended himself by saying he deliberately wrote immoral and heretical plays in order to challenge the public to reconsider its morals. Exactly 100 years later, we will be doing the same thing: deliberately publishing a blasphemous statement, in order to challenge the government to reconsider this absurd law."

Mathews said he supported Nugent's stance on publishing blasphemy and predicted a Life of Brian-style fate for his old friend. "Ideally I'd like to see Mick stoned to death for the crime of blasphemy. It would be tough to see him go, but I would be turning up to the stoning just for the sheer fun of it," he said. Mathews may be about to get into trouble himself - not over blasphemy but his new take on the Irish famine. His latest film, to be released in August, stars Fr Dougal, aka Ardal O'Hanlon, from Father Ted, and is set in a famine theme park in the Republic that includes a cafe for tourists. O'Hanlon, playing a drifter who gets a job in the theme park, has to dress up as a starving Irish peasant from the 1840s.

Atheist Ireland meanwhile said it would finalise plans for a blasphemous statement at its annual meeting, which is open to the public, in Wynns Hotel in Dublin next Saturday. Under the new law, anyone found guilty of blasphemy in the wider Defamation Act can be fined up to €25,000 (£21,400).